1) The current flow in a branch circuit is to be checked to determine if it is within the rated capacity of the circuit. The instrument best suited for this test would be:
a clip-on ammeter
2) Which of the following can be used to provide information about the shape of a voltage waveform?
- oscilloscope
3) The type of screwdriver designed for use on screws with an X-shaped insert in their heads is:
a Phillips screwdriver
4) An electromechanical relay is basically:
an electromagnet used to switch contacts.
5) Relays are primarily used to switch currents in the:
load circuit
6) Which of the following is not a common application for a relay?
change alternating current to direct current
7) A particular relay is rated as follows: coil-9V DC, 200 mA: contacts-120 V AC, 10 A. What maximum number of 100-W, 120-V light bulbs could be safely controlled by this
12
8) A particular relay is rated as follows: coil-9 V DC, 200 mA; contacts-120 V AC, 10 A. The resistance of the coil would be:
45
9) For an electromechanical relay, the amount of voltage and current required to energize the relay coil is:
more than what is required to de-energize the coil
10) Relays with sets of contacts, which are closed by some type of magnetic effect, are called:
electromechanical relays.
11) Relays with no contacts, which are switched entirely by electronic devices, are called:
solid-state relys
12) Solid-state relays use ____ as switching devices.
semiconductors
13) Which of the following is not an advantage of solid-state relays over electromechanical relays?
less susceptible to damage from voltage and current spikes
14) The purpose of overload protection on a motor is to protect:
the motor from sustained overcurrents.
15) The current drawn by a motor is:
both b and c
16) Which of the following is designed to provide machine operation protection by requiring the motor to be restarted after a power failure?
low-voltage protection
17) A contactor differs from a relay in that:
its contacts can interrupt large motor currents.
18) Technician A says a reduced-voltage starter is designed to apply full line voltage to the motor upon starting. Technician B says reduced-voltage starting produces a lower starting torque. Who is correct?
Technician B only
19) Which of the following starters increases the voltage gradually as the motor starts?
solid-state starter
20) Which of the following applies to stopping a motor by electronically reversing the motor while it is still running in the forward direction?
Plugging
21) Motor drive systems are used:
all of these
22) Which of the following is not a characteristic of AC motors?
high torque at low speed
23) In a variable-speed drive for a three-phase motor, which of the following circuits changes the DC power back to an adjustable frequency AC output?
Inverter
24) Sensors are used to detect the presence of and/or measure:
all of these
25) The insulating material on a printed circuit board is called:
the laminate.
26) The foil pattern layout for a PC board shows:
all necessary conductor routing required for the working circuit.
27) Resist is any material which:
will resist the chemical reaction used to etch copper.
28) The most commonly-used solder for soldering component leads to a PC board is:
60/40 resin-core wire solder.
29) A properly-soldered PC board connection will:
All of these
30) Large components that require considerable mounting space on a PC board are usually
left off the board completely and hand-wired.
31) When drilling lead access holes in a PC board:
moderate pressure should be applied to the drill.
32) For mass production of printed circuit boards, the type of printing process most often used is:
the photo-etch method.
33) When soldering on a PC board, the solder is always applied to:
the junction of the lead and the terminal pad area.
34) Cleaning the copper foil of a PC board prior to soldering:
is essential in all instances.
35) A computer is basically a digital electronic system.
True
36) Computers are capable of storing large amounts of data.
True
37) Nonvolatile memory loses all its information when power is removed.
False
38) The computing power of a computer is determined by its wattage rating.
True
39) All computers are able to get data into and out of memory at approximately the same speed.
True
40) The input/output provisions for microprocessor-based systems are all basically the same.
False
41) The microprocessor uses only analog signals.
False
42) Types of output devices include instrumental displays and actuators.
True
43) MS-DOS is an example of a programming language.
False
44) Word processing is a type of computer applications software.
True
45) In any number system, the position of a digit that represents part of the number has a weighted value associated with it.
True
46) To express a number in binary requires fewer digits than in the decimal system.
False
47) Most digital logic circuits are constructed using integrated circuits.
True
48) Combinational logic circuits have no memory.
True
49) The primary function of a combinational logic circuit is to make decisions.
True
50) The only true mathematical operation performed by a computer is division.
True
51) The state of a flip-flop is determined by observing its Q output.
True
52) In a D flip-flop, the Q output is the same as the D input one clock pulse later.
True
53) Asynchronous is the term used to designate control by a clock pulse.
True
54) Binary counters are usually constructed using XOR gates.
False
55) An integrated circuit:
is a complete electronic circuit with all components and interconnecting wiring contained within a single chip of silicon.
56) Which of the following IC packages is extremely vulnerable to damage from static electricity?
MOS
57) The use of ICs:
permits very complex circuits to have small physical dimensions.
58) Digital ICs contain:
switch-type circuitry.
59) Analog ICs contain:
amplifying-type circuitry.
60) The operational amplifier (op-amp) is:
all of these
61) The output power rating of an op-amp:
both a and c
62) An IC voltage comparator is basically:
an op-amp operated without a feedback circuit.
63) A 555 Timer IC is connected as a free-running oscillator. How can the output frequency be increased?
decrease the capacitance of the timing capacitor
64) Technician A says the duty cycle of a pulse waveform is the percentage of the time the output is high. Technician B says the duty cycle of a pulse waveform is found by dividing the total ON time by the total OFF. Who is correct?
Technician A only
65) When troubleshooting most electronic circuits, loading effect can be minimized by using a voltmeter with a/an:
input impedance much greater than the impedance across which the voltage is being measured
66) A semiconductor that decreases in resistance with an increase in temperature is known as a:
Thermistor
67) The shunt used in an ammeter should be connected in.
series with the load and in parallel with the meter movement
68) External shunts are sometimes used with ammeters to:
prevent damage to the meter movement from heat generated by the shunt
69) Which of the following statements represents an application of a silicon controlled rectifier?
To provide DC power for a main propulsion motor.
70) An accidental path of low resistance, allowing passage of abnormal amount of current is known as a/an :
short circuit
71) A resistance in a circuit of unknown value is to be tested using the voltmeter/ammeter method. Therefore, the meters should be connected with :
the ammeter in series and the voltmeter in parallel with the resistance
72) A direct current passing through a wire coiled around a soft iron core is the description of a simple :
Electromagnet
73) The use of four diodes, in a full-wave bridge rectifier circuit, will :
provide unidirectional current to the load
74) When troubleshooting electronic equipment, you should use a high impedance multimeter :
so as not to load down the circuit and obtain erroneous voltage readings
75) Which of the listed devices is used to measure pressure and convert it to an electrical signal ?
Transducer
76) The device that most commonly utilizes the principle of electromagnetic induction is the :
Transformer
77) Which of the following statements concerning analog and digital devices are correct?
The variables in digital systems are fixed quantities, and the variables in analog systems are continuous quantities.
78) The Wheatstone bridge is a precision measuring instrument utilizing the principle of changes in :
Resistance
79) Which of the listed logic gates is considered to be a BASIC building block (basic logic gate) used in logic diagrams?
OR
80) Heat sinks are frequently used with :
Power transistors
81) The first requirement for logical troubleshooting of any system is the ability to :
recognize normal operation
82) A fuse that blows often should be replaced only with a fuse of :
the recommended current and voltage rating
83) Which of the listed conditions is an advantage of a PN diode over a vacuum diode?
All of the above.
84) The heating of conductors as a result of resistance in a distribution circuit causes a power loss expressed as :
line loss
85) In process control terminology values which can change without distinct increments, such as temperature, pressure, or level are called :
analog values
86) Silicon diodes designed for a specific reverse breakdown voltage, become useful as an electronic power supply voltage regulator, called :
Zener diodes
87) The type of feature afforded auxiliaries vital to the operation of propelling equipment, where automatic restart after a voltage failure would not create a hazard, is termed :
low voltage release
88) Which of the following statements correctly applies to transistors?
The three terminals are called the emitter, base, and collector.
89) The basic measuring unit of inductance is the :
Henry
90) Alternating current circuits develop resistance, inductance and capacitance. The inductance of a coil is expressed in :
Henrys
91) An insulation resistance test is performed on a particular piece of electric equipment. In addition to the resistance reading, what information listed below should be entered in the electrical log?
The temperature of the machine at the time the resistance reading was taken.
92) Alternating current circuits develop resistance, inductance, and capacitance. The capacitance of individual capacitors is expressed in :
Farads
93) Which of the following statements represents the important factor that must be considered when replacing a faulty diode in the exciter rectifier assembly?
Be certain that the replacement diode is the same polarity as the one removed.
94) The insulation resistance of electric equipment and machinery should be tested for the lowest normal insulation values :
immediately after shutting down the machine
95) A triac thyristor functions as a control device and is basically :
two back-to-back SCRs with a common gate lead
96) The apparent power in a purely inductive circuit is also known as :
reactive power
97) The multiple prefix giga (G) means :
billion (10 to the 9th power)
98) Copper is often used as an electrical conductor because it :
is able to pass current with little opposition
99) The unit of apparent power in a purely inductive circuit is called the :
Var
100) A grounded switch or cable will be indicated by a megohmmeter reading of :
zero
101) The multiple prefix kilo means :
thousand (10 to the 3rd power)
102) An adjustable resistor, whose resistance can be changed without opening the circuit in which it is connected, is called a :
Rheostat
103) The purpose of a heat sink, as frequently used with transistors, is to :
prevent excessive temperature rise
104) The combined effect of inductive reactance, capacitive reactance, and resistance in an AC series circuit is known as :
Impedance
105) In a DC series circuit, all the conductors have the same :
current passing through them
106) AC circuits develop resistance, inductance, and capacitance. The inductive reactance of a circuit is expressed in :
Ohms
107) A silicon controlled rectifier (SCR) is a solid state device used to change :
AC to DC and control relatively high load current
108) The basic control action of a magnetic amplifier depends upon :
changes in inductance
109) The process, whereby electrons gain sufficient energy to be released from the surface of a thin, heated metal plate, is known as :
thermionic emission
110) Most conducting materials such as copper, aluminum, iron, nickel, and tungsten :
increase in resistance with increased temperature
111) In a series circuit, which value will remain unchanged at all places in the circuit?
Current
112) In electronic circuitry, the abbreviation PCB commonly means ______________.
printed circuit board
113) Which of the listed conditions describes the effect on intrinsic semiconductor operation as a result of a temperature increase?
Conductivity will increase
114) In electronic circuits, DC voltages can be positive (+) or negative (-) when measured with respect to the :
all of the above
115) Capacitors are used on the output of the power supply in todays consoles to :
filter out ripple
116) Operational amplifiers, used primarily in analog circuits, are characterized by :
high input impedance, high gain and low output impedance
117) Reversing the current flow through a coil will :
reverse its two-pole field
118) The schematic symbol for an operational amplifier in an analog circuit is a :
Triangle
119) The total resistance of a parallel circuit is always :
smaller than the lowest branch resistance
120) Which of the following expresses the relationship of the input and output frequencies in a full wave rectifier?
The output frequency is twice the input frequency.
121) A temperature instrumentation system for an engine room console consists of a resistance temperature detector (RTD), a measuring bridge circuit, and a meter (or alarm circuit).Which of the following statements is true concerning the measuring bridge circuit :
The resistance bridge is said to be balanced when its output voltage is zero.
122) One feature of the operational amplifier is that it can have :
inverting and non-inverting inputs
123) A signal derived from a controlled function and returned to the initiating point is called a/an :
feedback signal
124) A semiconductor is a material with a :
conductivity higher than a normal insulator
125) A capacitor can be tested using a megohmmeter or an ohmmeter. If the meter is connected to a shorted capacitor, the meter pointer should :
immediately deflect to and remain at zero
126) To provide its unique characteristics to analog circuits, the operational amplifier is made up of a/an :
differential amp, voltage amp and output amp
127) When replacing a power transistor fitted with a heat sink in a circuit, a coating of silicone grease is applied between the transistor case and the heat sink. This is done to :
provide maximum heat transfe.
128) The resistance of a conductor varies :
directly as its length and inversely as its cross-sectional area
129) In order to check the performance of a transistor removed from its circuit, the instrument to be used should be a/an :
- ohmmeter or transistor tester
130) When a megohmmeter is being used to test insulation resistance, current leakage along the surface of the insulation is indicated by the megohmmeters pointer :
kicking slightly down scale as voltage is applied
131) Which of the following actions can be carried out in order to prevent thermal runaway in a transistor?
Install a heat sink.
132) Basic operating characteristics of the operational amplifier such as gain and stability are the function of its :
feedback circuit
133) Possible phase relationships between voltage and current in an alternating current circuit include which of the following conditions?
All of the above.
134) A suspected open in a motor field can be tested by using a/an :
Ohmmeter
135) The sub-multiple prefix nano (n) means :
billionth (10 to the -9th power)
136) A switchboard, for a AC electrical distribution system, will be provided with which of the following components?
All of the above
137) Which of the procedures listed could result in damaging a transistor beyond repair?
All of the above.
138) Basically, a magnetic amplifier is a saturable reactor with the addition of :
a rectifier in the load circuit
139) Which of the electrical properties listed will always be the same for each component in a parallel circuit?
Voltage
140) Which of the listed instruments can be best used to locate a grounded field coil in a synchronous motor?
Megohmmeter
141) A capacitor discolored due to excessive heat should be :
Replaced
142) A covalent bond:
all of these
143) If a silicon crystal is doped with a material having five valence electrons:
an N-type semiconductor is formed.
144) If a germanium crystal is doped with a material having three valence electrons:
a P-type semiconductor is formed.
145) In a PN-junction diode, the depletion region is formed by:
electrons crossing the junction and filling the holes.
146) A PN-junction diode is said to be forward- or reverse-biased depending on:
the polarity of the DC voltage applied across it.
147) Excessive reverse-bias voltage may cause a silicon diode to:
avalanche.
148) When checking a diode with an ohmmeter, a good diode would be indicated by:
a low-resistance reading in the one direction and a high-resistance reading in the other.
149) A diode rated for 35-V peak forward-bias voltage is used in a circuit rated for a peak forward-bias voltage of 24 V. The diode will:
- operate normally.
150) A light-emitting diode (LED) will:
all of these
151) The laser diode has a(n) ____ which is required for lasing production.
- optical cavity
152) The three leads of a bipolar junction transistor are:
the base, the collector, and the emitter.
153) Field-effect transistors (FETs) operate:
with a small input voltage but practically no input current.
154) The PNP transistor is the complement of the NPN transistor. This means:
that the two are electrically similar except that opposite current and voltages are involved.
155) A bipolar-junction transistor circuit is operated so that:
a small change in base current controls a large change in collector current.
156) The drain current produced by a properly biased N-channel junction FET will decrease when the FETs gate is:
made more negative with respect to its source.
157) The input resistance of a junction FET will remain extremely high as long as the FETs gate-to-channel junction is:
reverse-biased.
158) An insulated-gate FET will maintain a high input resistance when its gate is made:
positive or negative with respect to its source.
159) To protect MOSFETs against static charges:
both b and c
160) A unijunction transistor (UJT):
does not amplify.
161) When a UJT switches to the ON state, current is conducted between:
emitter and base 1.
162) The main application for SCRs and triacs is:
for control of power in the watt or kilowatt range.
163) A silicon-controlled rectifier (SCR) is normally biased so that it can be turned ON by:
momentarily applying a gate current.
164) When an SCR circuit is operated from an AC source:
both a and c
165) In order for an SCR to be triggered into conduction:
both the anode and the gate must be positive with respect to the cathode.
166) SCR phase-shift control circuits are used to vary the ____ between the trigger pulse and the point in the conducting cycle when the pulse occurs.
time relationship
167) ____ of the positive half-cycle will be conducted to the load, depending on when the SCR fires.
all of these
168) How is a silicon-controlled rectifier similar to a diode rectifier?
Both conduct current in one direction only.
169) The main difference between the operation of an SCR and a triac is:
an SCR can be triggered into conduction in only one direction.
170) An out-of-circuit ohmmeter check of a non-defective 24-V diac should indicate:
a high resistance reading in both directions.
171) Breakover voltage of a diac is:
the point at which its resistance changes from high to low.
172) The joule is the base unit of:
Work and energy
173) The part of the atom that has no electric charge is the:
Neutron
174) A positive charge can:
both of the above
175) The nucleus of most atoms contain:
both of the above
176) A negative ion has an excess of:
Electrons
177) A proton has:
a positive electric charge
178) Electrons in the outermost shell of an atom are called:
valence electrons
179) When an electron becomes a free electron its energy level is:
none of the above
180) The base unit of charge is the:
Coulomb
181) The joule is the base unit of:
Energy
182) Kilowatthour is a unit of:
Energy
183) A wattsecond is equal to a(n):
Joule
184) The charge possessed by 6.25 x 1018 electrons equals one:
Coulomb
185) A coulomb per second equals the base unit of:
Current
186) Joule per coulomb is the definition of a:
volt
187) The amount of resistance is expressed in:
Ohms
188) A current of 0.04 A could also be expressed as:
40 mA
189) In addition to Ohm’s law, solving multiple-load circuits requires the use of:
Kirchhoff’s laws
190) The formula that can be used in any type of circuit is:
PT = PR1 + PR2 + PR3 + etc.
191) RT is always greater than R1 in:
a series circuit
192) IR1 is always less than IT in:
a parallel circuit
193) A condition that is necessary for maximum power transfer is:
Rsource = Rload
194) The smallest resistance always dissipates the most power in:
a parallel circuit
195) The largest resistance always drops the most voltage in:
a series circuit
196) For the circuit below, PT is equal to:
320 mW
197) For the circuit below:
all of the above
198) For the circuit below:
neither of the above
199) Solving simultaneous equations requires:
as many independent equations as there are unknown variables
200) The technique that can’t be used on single-source circuits is:
superposition theorem
201) The technique that can’t be used on multiple-source circuits is:
none of the above
202) The technique that uses only series-parallel rules and procedures is:
superposition theorem
203) The technique that may not determine all current and voltage values is
Norton’s theorem
204) The technique that may require the use of another technique before it can be applied is:
Thevenin’s theorem
205) The technique that requires only one calculation to determine the new load current when the load resistance is changed is:
Norton’s theorem
206) The technique that may yield a negative value of current is:
loop equations
207) Determine the value of IR2, IR3, and VR2 in the circuit below.
IR2 = 1.25 mA, IR3 = 1.75 mA, VR2 = 3 V
208) The direction of the flux around a conductor can be determined by:
either of the above
209) The invisible lines of force around a magnet are called:
magnetic flux
210) When the currents in two parallel conductors are in the same direction:
the conductors attract each other
211) The most magnetic element is:
Iron
212) Increasing the space between the turns in a coil:
decreases the flux at the poles
213) The flux associated with a temporary magnetic material after the material is removed from a magnetic field is called:
none of the above
214) The unit used to specify flux density is the:
Tesla
215) The unit for permeability is the:
none of the above
216) Magnetic shields are usually made from:
temporary magnetic materials
217) The most common waveform for ac is the:
sine wave
218) One cycle of an ac waveform:
both of the above
219) The rate at which cycles are produced is called the:
Frequency
220) One cycle per second is equal to:
a hertz
221) Unless otherwise specified, ac values are assumed to be:
effective values
222) One cycle spans:
360 electrical degrees
223) The phase voltages in a three-phase system are separated by:
120 electrical degrees
224) When the T = 2 ms, f will equal:
500 Hz
225) The f of an eight-pole generator rotating at 600 r/min will be:
40 Hz
226) In a wye-connected three-phase system, the relationship between the magnitudes of the phase and the line voltages is:
Vline = 1.732 Vphase
227) The particles that can be found within an atom are:
neutrons, protons, and electrons.
228) The smallest negative particle of electricity is called:
an electron.
229) The weight of a proton is:
much greater than that of an electron.
230) A negatively charged ion has:
more electrons that protons.
231) The outer-shell electrons of an atom:
all of these
232) Electrons are held in their orbital path by:
centrifugal forces counterbalancing attraction forces.
233) A good insulator of electricity is a substance that:
is used to prevent the flow of electrons.
234) A transistor can be classified as:
a specially-treated semiconductor.
235) A continuity tester is basically:
a series circuit consisting of a battery, light bulb, and test leads.
236) A continuity tester is used to check a fuse. When the fuse is connected across the test leads, a blown fuse is indicated when:
the lamp does not come on at all.
237) Static electricity is:
an electrical charge at rest.
238) When a hard rubber rod and a piece of fur are rubbed together, the fur gives up electrons to the rubber rod. As a result:
the rod becomes negatively charged.
239) The law of electric charges states:
like charges repel, unlike charges attract.
240) Current electricity:
is an electric charge in motion.
241) When a charge is transferred without direct physical contact, this is known as charging by:
induction.
242) When an alternating current power source is connected to a circuit, it produces a current that:
changes in both direction and magnitude.
243) Voltage is produced in a battery by means of:
a chemical reaction.
244) A device that produces a voltage when put under pressure is:
a crystal.
245) Large amounts of electricity are usually produced using:
a generator.
246) In the battery, or voltaic cell, electrons are transferred from one electrode to the other. The electrode that gains electrons is:
the negative terminal.
247) Technician A says that when taking measurements with a voltmeter and an ammeter, the meters are both connected into the circuit in the same way. Technician B says the voltmeter is connected in series and the ammeter is connected in parallel. Who is correct?
neither Technician A nor Technician B
248) The force that causes the flow of electrons through a conductor is known as:
the voltage.
249) The unit of measurement for the difference of potential between two points is:
the volt
250) An electric toaster is rated for 220 V and 10 A. Its power rating would be:
2200W
251) Which of the following is an example of a voltage source?
a battery
252) In a basic electrical circuit, the part that stores electric energy or changes it into other forms is:
the load.
253) Electrical conductors:
complete the electron path from the source to the load.
254) Which of the following is an example of a load?
a hair dryer
255) Which of the following is classified as a protective device?
both b and c
256) A switch would be classified as:
a control device
257) A poorly made electrical connection:
all of these
258) For practical purposes, all the circuit resistance is considered to be contained in:
the load device.
259) The purpose of the energy source is to:
supply the voltage required to move the free electrons
260) A fuse is used to:
all of these.
261) Which of the following electrical diagrams is easiest to read?
Schematic
262) A string of lamps is connected in parallel to a voltage source. If one lamp burns out, all the other lamps:
will not be affected.
263) A string of lamps are connected in series to a voltage source. This connection would result in:
- one current path.
264) An AND-type control circuit consists of switches connected in:
series.
265) If a circuit is constructed to allow the electrons to follow only one possible path, the circuit is called:
a series circuit
266) Two switches are connected to control a lamp. A ____ can be used to show how the switches work the lamp.
truth table
267) Replacing a fuse with one of a higher current rating can cause:
wiring to overheat.
268) One of the factors involved in an electric shock is body resistance. Which of the following statements about body resistance is not true?
The higher the body resistance, the greater the potential shock hazard.
269) Generally, any voltage above ____ V is considered dangerous.
48
270) The severity of an electric shock increases with:
all of these
271) Resistance wire is designed primarily to convert electricity energy into:
Heat
272) When a resistor has a 2-W rating, this means that it:
can safely dissipate 2 W, or less, of power.
273) Which resistor would you choose if you were asked to pick a resistor to use on a printed-circuit board circuit in which a large number of identical resistors were required?
resistor network
274) Which of these variable resistors would most likely be used to control current in a higher power-level circuit?
Rheostat
275) A voltage divider is formed by connecting a 6-kΩresistor and a 2-kΩ resistor in series across a 20-V source. The voltage drop across each resistor would be, respectively:
15 V and 5 V
276) The symbol for the prefix micro (metric measure) is:
μ
277) A 470,000 Ωresistor may be designated as:
470 kΩ
278) Converting 1 mA to its base unit produces:
0.001 A
279) A voltage of 0.48 V can be expressed as:
480 mV.
280) Ohms law states that:
current is directly proportional to the voltage and inversely proportional to the resistance
281) Technician A says that in a electrical circuit, voltage can exist without current. Technician B says that current cannot exist without voltage. Who is correct?
both Technician A and Technician B
282) How much current will a 0.75 Ω car rear window defogger draw when connected to a 12-V battery source?
16 A
283) The current flowing through a 72 Ω resistor is measured and found to be 0.5 A. How much voltage is being applied across the resistor?
36 V
284) What is the resistance of a soldering iron element that conducts a current of 4 A when connected to a 120-V electric outlet?
30 ohm
285) If a voltage of 3 V is applied across a resistor of 9 Ωhow many watts of power does the resistor dissipate?
1 W
286) A series circuit has:
- one pathway for current flow.
287) In a series circuit, the amount of voltage each load receives is:
directly proportional to the resistance value of the load.
288) Three resistors (R1, R2, and R3) are connected in series to a 120-V source. The values of V1 and V3 are measured and found to be 42 V and 8 V, respectively. The value of V2 would then be:
70 V
289) How much resistance R1 must be added in series with a 400 ΩR2 to limit the current to 0.25 A with 120 V applied?
80 Ω
290) Resistors R1 - 8 kΩ, R2 - 4 kΩ, R3 - 6 kΩ, and R4 - 2 kΩare connected in series to a voltage source. Which resistor will dissipate the most power?
R1
291) Three resistors with values of 1 kΩ, 5 kΩ, and 3 kΩ, respectively, are connected in series with a fourth resistor of unknown value. The applied voltage is 120 V and the current flow is 5 mA. What is the resistance value of the unknown resistor?
15 kOhm
292) A string of twelve holidy lamps is designed to be connected in series to a 120-V source. If one of the lamps burned out and was shorted from the circuit, the operating voltage across each of the other eleven lamps would be:
10.9 V
293) Which resistor of a series circuit receives the largest voltage drop?
the one with the most resistance
294) The polarity of the voltage drop across a resistor depends on:
the direction of current flow through it.
295) Two voltage sources are connected series-opposing. Technician A says the two voltages are added to obtain the total equivalent voltage. Technician B says the equivalent voltage is given the polarity of the greater voltage. Who is correct?
Technician B only
296) With 24 V applied across five 6 Ω resistors in parallel, the total current equals ____.
10 A
297) With two resistances connected in parallel, if each dissipates 5 W, the total power supplied by the voltage source equals:
10 W
298) With two resistances connected in parallel:
the voltage across each must be the same.
299) Resistors of 10 Ωand 30 Ωare connected in parallel to a 120-V supply. The current flow through the 10 Ωresistor would be:
12 A
300) A three-branch parallel resistor circuit is connected to a 6-V source. The branch currents are 1.2 A, 800 mA, and 250 mA, respectively. The total current is:
about 2.25 A
301) Four resistors, 1 kΩeach, are connected in parallel. This group is connected to a 9-V source. The combined resistance of the group is:
250 Ohm
302) Four resistors, 1 kΩeach, are connected in parallel. This group is connected to a 9-V source. The current in the line leading to the group of resistors is:
36 mA
303) The voltage across an open component in a parallel circuit is always equal to:
the source voltage
304) With a short in one of the branches of a parallel circuit:
all of these
305) Technician A says that in a parallel circuit, a shorted resistor shorts out the entire circuit. Technician B says this can burn out the power supply unless the circuit is protected by a fuse or a circuit breaker. Who is correct?
both Technician A and Technician B
306) Consider the circuit in Figure 1. The known voltages and currents are as indicated. Applying Kirchhoffs voltage and current laws, the value of the voltage drop across R2 would be:
40 V
307) Consider the circuit in Figure 2. The known voltages and currents are as indicated. Applying Kirchhoffs voltage and current laws, answer the following question. The value of the applied voltage source would be:
9 V
308) The value of the voltage drop across R4 Figure 2 would be:
9 V
309) The value of the current flow through R1 Figure 2 would be:
1.5 mA
310) Answer the following question with reference to the series-parallel circuit in Figure 3.
10 Ohm
311) The total power dissipated by the circuit in Figure 3 is:
1440 W
312) The total current flow of the circuit in Figure 4 is:
12 mA
313) The total current flow of the circuit in Figure 5 is:
1.5 A
314) The current flow through resistor R2 in Figure 5 is:
1 A
315) If resistor R1 in Figure 5 becomes short-circuited, the total resistance of the circuit will:
be zero.
316) Three substances that are classified as magnetic materials are:
steel, nickel, and cobalt.
317) The lodestone is a natural form of a:
permanent magnet
318) Soft iron is most suitable for use in a:
temporary magnet.
319) Artificial magnets can be produced by:
placing magnetic material in the core of a coil and applying a DC voltage to the coil.
320) The magnetic force between two poles:
increases as the distance between the two poles decreases.
321) Permanent horseshoe-shaped magnets:
provide a much stronger magnetic field than a bar magnet of equal material.
322) A permanent ring magnet:
both b and c
323) A material that acts as an insulator for magnetic flux is:
unknown today
324) Which of the following is not assumed to be a characteristic of magnetic lines of force?
They travel most easily through air.
325) Which of these does not normally have a demagnetizing effect?
DC applied to a coil
326) A DC current flow through a conductor will produce:
either a or b
327) The left-hand conductor rule is used for a current-carrying conductor to determine the:
a direction of the lines of force around the current-carrying conductor.
328) Lines of force of two parallel conductors with current flows in opposite directions will:
- oppose each other to produce a weaker field.
329) If the electromagnet is operated with direct current, the polarity of its magnetic poles:
remains fixed.
330) The advantage of a toroidal core over a straight core is that the toroid is:
self-shielding.
331) If other factors remain constant, which of the following combinations of electric current and the number of turns in the coil produces the strongest electromagnet?
700 turns and 2 A
332) The magnetic circuit consists of:
lines of force travelling from the N pole to the S pole.
333) Consider the following changes made to an electromagnet: (i) increasing the number of turns in the coil; (ii) using a copper core instead of an iron core; (iii) decreasing the current flow in the coil. The strength of the electromagnet is increased by:
(i) only.
334) A solenoid can be classified as an electromagnet with:
a moveable iron core.
335) Solenoids can be used to operate:
all of these
336) Generating stations are classified according to:
the method used to drive their generators.
337) The cheapest and most environmentally-safe type of generating station is:
a hydroelectric generating station.
338) Which of the following converts the suns energy directly into electrical energy?
silicon wafer
339) Transmitting electrical energy from the generating station to the consumer usually takes place at:
very high AC-voltage levels.
340) Electrical transmission power-line losses are kept to a minimum by:
using a high voltage and a low current.
341) The unit used to measure electric power is:
the watt.
342) When a 12-V battery delivers 18.0 A of current the power supplied is:
216 W.
343) What is the power rating of an electric dryer element which has a resistance of 7.2 Ohm and is rated for 240 V?
7200 kW
344) A wattmeter is connected:
with the ammeter section in series and the voltmeter section in parallel with the load.
345) A wattmeter is connected into a circuit and the pointer moves in the reverse direction. The problem can be corrected by:
either a or b
346) Technician A says electric energy is measured in joules. Technician B says it is measured in kilowatthours. Who is correct?
both Technician A and Technician B
347) An electric lamp transforms electric energy into:
both b and c
348) How much energy is consumed when a 2000-W electric device is left on for 1 h?
2 kWh
349) The amount of electric energy used for electric appliances depends on:
both b and c
350) Which of the following electric devices has, on an average, the highest annual energy consumption?
a range
351) Alternating current is current that:
- operates from a voltage source that has a constantly reversing polarity.
352) Generating a voltage by rotating a coil at a constant rate through a magnetic field results in a voltage that:
both a and b
353) The standard frequency of the AC voltage available from the electric outlet in your home is:
50 Hz
354) If a sine wave has a peak-to-peak voltage value of 60 V, what is the rms value?
21.2 V
355) If a sine wave has a peak value of 220 V, what is the rms value?
155 V
356) For any given generator the output voltage varies:
directly with its speed and the strength of the magnetic field.
357) In an automobile alternator the three-phase AC stator voltage is converted to DC using:
Diodes
358) The value of inductance is expressed in ohms.
False
359) In AC circuits the ohmic value of resistive elements depends on the frequency of the AC.
False
360) A resistance of 6Ω in series with 14Ω of reactance results in an impedance of 20Ω.
False
361) The capacitive voltage can be higher than the source voltage is a series RLC circuit.
True
362) The cut-off frequency determines if the filter is a low-pass or high-pass filter.
False
363) The total opposition to current flow in an AC circuit is called :
Impedance
364) The true power in a resistance is measured in :
Watts
365) In a series resonant band-pass filter where: fr = 100 Hz, f1 = 95 Hz, f2 = 105 Hz, the bandwidth is _____.
10 Hz
366) A series RLC circuit is _____ when XL is greater than XC.
Inductive
367) When a Norton equivalent circuit is converted to Thevenin equivalent circuit RTH will be equal to RN.
False
368) A Thevenin equivalent circuit represents an ideal (constant) voltage source.
True
369) When VRL for many values of VL must be determined, a circuit should be thevenized.
True
370) Current is independent of load resistance for a current source.
True
371) Nortons theorem reduces a resistive network to an ideal current source and a parallel resistance.
True
372) If two currents are in opposing directions through a branch of a circuit, the direction of the net current will be the same as that of the smaller current.
False
373) What is the Norton resistance as viewed by RL for the circuit below?
3 Ohm
374) Find the Thevenin resistance, as viewed by RL, for the circuit drawn below.
25 Ohm
375) Find the Thevenin voltage, as viewed by RL, for the circuit drawn below.
25 V
376) What is the Norton current as viewed by RL for the circuit below?
6 A
377) A trilight or dual filament lamp is rated for 40-60-100 W. This bulb would contain:
- one 40-W and one 60-W filament.
378) The best way to test an incandescent lamp filament is:
to check it for continuity with an ohmmeter.
379) The resistance of a 200-W, 120-V incandescent lamp would be:
lower than that of a 40-W, 120-V incandescent lamp.
380) Recessed ceiling fixtures require special installation safety procedures because:
they have very poor ventilation.
381) Which of the following is not an advantage of fluorescent lamps over the incandescent types?
lower initial cost
382) The fluorescent bulb produces light by:
means of an electron arc established between two cathodes.
383) The instant-start fluorescent tube:
all of these
384) A cycling ballast that turns power OFF and ON is most likely caused by:
an overheated ballast.
385) Which of the following is not an advantage of high-intensity discharge lamps?
They operate at low current.
386) High-intensity discharge lamps:
- operate at low brightness when first turned on.
387) In an ideal inductor:
current lags the voltage by 90?.
388) Energy is stored in a capacitor by means of:
its electrostatic field.
389) As applied to a capacitor, the word dielectric refers to:
the insulating material separating the plates.
390) Polarized fixed capacitors must be connected:
with the positive lead of the capacitor connected to the positive lead of the circuit.
391) Which indication on an ohmmeter should you most likely expect when testing a good capacitor?
momentary upscale pointer deflection
392) Approximately what percentage of the applied voltage does the capacitor charge to at the end of the first time constant?
63 percent
393) A 50- F capacitor is connected to a 120-V, 60-Hz source. The capacitive reactance of this capacitor would be approximately ____ ohms.
53
394) In general, impedance has an effect on an AC circuit similar to:
resistance.
395) Impedance may be defined as:
the total opposition to current flow in an AC circuit.
396) Lagging power factor is often produced by:
all of these
397) A transformer is a device used to:
transfer electric energy by mutual induction.
398) An iron core is used in a transformer to:
ensure good magnetic linkage between windings.
399) A step-down transformer is used to change:
high voltage to low voltage.
400) The transformer used with a certain model car set has 240 turns in its primary coil and 24 turns in its secondary coil. If the transformer is connected to a 120-V wall receptacle the secondary voltage output would be approximately:
12-V AC.
401) Most transformers operate to transfer energy at an efficiency of about:
95 percent.
402) A certain transformer has a turns ratio of 1:1. The transformer is used for:
isolation.
403) Power transformers are designed to operate:
from 60-Hz line frequency.
404) Which of these would most likely be used to match a 4- speaker to a 400-- amplifier output?
audio impedance-matching resistor
405) A transformer coil can be checked with an ohmmeter for:
continuity.
406) The rated input and output voltages of a transformer are checked with a voltmeter. Technician A says a normal primary voltage reading and no secondary voltage reading is an indication of an open secondary coil. Technician B says it is normal for the transformer output voltage to be higher than specified if no load is connected to the output. Who is correct?
both Technician A and Technician B
407) The purpose of a power supply is:
to convert the electrical input voltage to the proper type and value needed to operate circuits.
408) In a power-supply circuit the transformer can be used to:
all of these
409) A step-down transformer will have:
a higher primary than secondary voltage.
410) A step-up transformer will have:
all of these
411) A standard transformer can safely isolate a 120-V primary circuit from a 10-V secondary circuit because:
no physical electrical connection exists between the primary and secondary coils.
412) What is the output ripple frequency of a bridge rectifier?
twice the input frequency
413) The approximate DC voltage output of a full-wave rectifier is equal to:
0.637 of the peak output voltage.
414) Which of the following components is commonly used as a filter device?
a capacitor
415) Increasing the capacitance of the filter capacitor will have what effect on the ripple amplitude?
ripple will decrease
416) The voltage regulation of a power supply refers to:
the ability of a power supply to maintain a constant output voltage.
417) Voltage and current are in phase when the load contains:
nothing but resistance
418) Current and voltage will be 90 degrees out of phase when the load contains:
nothing but reactance
419) The magnitude and direction of an electrical quantity can be shown with:
neither of the above
420) Power is used by the
resistive part of a load
421) The unit for apparent power is the:
Voltampere
422) Current will lead voltage by 90 degrees when the load is:
pure capacitance
423) The numerical value of the cos O when the load contains only resistance is:
One
424) When the PF = 90%, the cos O is
0.900
425) When P = 500 W, I = 6 A, and V = 120 V, the PF will be:
0.69
426) When I = 4 A, P =300 W, and V= 240 V, angle theta will be:
71.8grd
427) A capacitor consists of two conductive plates separated by a(n):
both of the above
428) The base unit of capacitance is the:
Farad
429) Most electrolytic capacitors are:
polarized capacitors
430) The relative energy loss of a capacitor is specified by its:
any of the above
431) In one time constant, a capacitor charges to:
63.2 % of the available voltage
432)
20 V
433) CT for the circuit in question 6 will be:
0.8 uF
434) The reactance of a 0.022-uF capacitor at 500 Hz will be:
none of the above
435) For the circuit below, XCT will be:
318 Ohm
436) The energy stored in a 2000-uF capacitor when the capacitor is charged to 150 V is:
22.5 J
437) Inductance opposes any change in:
Current
438) According to Lenz?s law, the polarity of a cemf is such that the cemf always:
- opposes the force that created it
439) The base unit of inductance is the:
Henry
440) The dc resistance of an inductor is also known as its:
- ohmic resistance
441) Arcing in switch contacts that control an inductive circuit:
both of the above
442) The resistance of a conductor increases as frequency increases because of the:
skin effect
443) The induced voltage in an inductor is called its:
both of the above
444) The reactance of a 0.1-mH inductor at 2.1 MHz is:
none of the above
445) If the effective resistance is 20 Ohm, the Q of a 2.5-mH inductor at 30 kHz is:
23
446) IT for the circuit below is:
6.4 mA
447) The primary coil of a transformer:
none of the above
448) Copper loss in a transformer is also called:
I^2R loss
449) The portion of the primary flux that links with the secondary coil is specified by the:
coefficient of coupling
450) An isolation transformer:
all of the above
451) The currents induced in the core of a transformer are called:
eddy currents
452) Hysteresis loss in a transformer is caused by:
residual magnetism
453) When a transformer has 100% coupling:
the turns ratio is equal to the voltage ratio
454) One disadvantage of the autotransformer is:
it does not provide electrical isolation
455) A transformer can not be overloaded:
unless the VA rating of one or more windings is exceeded
456) A 4-Ohm resistive load connected to a source by a transformer with a 9:1 turns ratio will appear to the source as a:
324-Ohm resistive load
457) In a parallel RC circuit where R exceeds XC:
none of the above
458) In a parallel RC circuit where XC exceeds R:
IT will lead VT
459) In a series RC circuit where R exceeds XC:
Phi will be < 45grd
460) In a parallel RL circuit where R exceeds XL:
IT will lag VT
461) In a series RL circuit where XL exceeds
none of the above
462) In a parallel RCL circuit where XL = 250 , XC = 400 , and R =300 :
PT will = PR
463) In a series RCL circuit:
all of the above
464) What is the bandwidth of a circuit that is resonant at 470 kHz and has a Q of 90?
5.2 kHz
465) Determine Z and Phi for the circuit below.
924.6 , 59.4 grd
466) Determine the resonant frequency of a 270-uH inductor and a 220-pF capacitor.
653 kHz
467) Motors are not available in this size:
Mihp
468) Motors are usually not rated for:
power factor
469) Voltage-rating tolerance for motors is typically:
+/- 10%
470) For motor-design, ambient temperature is usually considered to be:
40grdC
471) With the highest class of insulation, a motor can operate at a temperature of:
180grdC
472) Which of these motors is synchronous?
Reluctance
473) Which of these motors has the least starting torque?
shaded-pole
474) Which of these motors has the most starting torque?
capacitor-starting
475) Determine the power for a dc motor that develops 3 lb-ft of torque at 2500 r/min.
1.43 hp
476) What is the synchronous speed of an eight-pole, 240-V, 50-Hz moto
750 r/min
477) The meter movement most often used in analog multimeters is the:
dArsonval movement
478) The meter movement used in the analog wattmeters is the:
electrodynamometer movement
479) A rectifier can convert:
alternating current to pulsating direct current
480) The range of an analog ammeter is determined by:
the value of the shunt resistor
481) The range of an analog voltmeter is determined by:
the value of the multiplier resistor
482) The sensitivity of a VOM is specified by its:
Ohm/V rating
483) Testing for minute leakage current in motors, transformers, etc. is done with:
an insulation tester
484) Digital meters measure inductance by measuring
the inductors cemf
485) Digital meters measure capacitance by measuring:
the time required to charge the capacitor
486) Digital meters measure frequency by:
counting the cycles per unit of time
487) Analog meters:
use a mechanical type of meter movement.
488) The multimeter:
all of these.
489) A reading of 4.7 kΩon the display of a digital multimeter indicates a resistance reading of:
4700Ω
490) A DC analog voltmeter can be used to measure an AC voltage if:
the incoming AC voltage is rectified.
491) An analog multimeter is connected to measure a DC voltage, and the needle reads below zero. The most likely cause is:
reversed polarity.
492) A milliammeter is designed measure:
lower values of current than an ammeter does.
493) To zero set an analog-type ohmmeter, adjust the zero-set knob for a pointer reading of:
zero with the meter-test leads connected together.
494) When using the ohmmeter as a continuity tester, an open circuit is indicated by:
an infinite-resistance reading.
495) Technician A says analog meters are more accurate than digital meters. Technician B says digital meters that use a light-emitting diode (LED) display have a longer battery life than those that use a liquid-crystal display (LCD). Who is correct?
neither Technician A nor Technician B
496) Auto ranging is a feature of a multimeter that:
automatically adjusts the meters measuring circuits to the correct range.
497) When using the oscilloscope you should avoid:
- operating it with a high-intensity spot displayed.
498) The waveform displayed on the screen of the oscilloscope represents a plot of:
voltage versus time.
499) The AC/DC switch of an oscilloscope:
selects how the input signal is coupled to the oscilloscope.
500) A signal displayed on the calibrated time base of the oscilloscope covers 1 cycle in 10 DIV with the TIME/DIV control set at 20 ms. The waveform frequency is:
5 Hz.
501) Technician A says when connecting the test probe of a scope to a grounded circuit, the grounded conductor of the probe is connected to the grounded side of the circuit. Technician B says the scope should never be used to test a grounded circuit. Who is correct?
Technician A only
502) A dual-trace oscilloscope:
has two sets of controls to control two different traces.
503) A digital storage scope allows you to:
all of these
504) The control of a signal generator used to adjust the voltage value of the output signal is:
the amplitude control.
505) Technician A says that a function generator can do all of the things an audio generator can do. Technician B says the function generator is more compatible with solid-state electronic circuitry than the audio generator. Who is correct?
both Technician A and Technician B
506) A DC power supply has a rated output of 3 W at 9 V. The maximum current rating of this power supply would be approximately:
333 mA.
507) Clasificarea sistemelor automate dupa structura lor
sisteme deschise; sisteme inchise;
508) Clasificarea sistemelor automate dupa cantitatea de informatie apriori disponibila
sisteme automat conventionale; sisteme adaptive;
509) Clasificarea sistemelor automate dupa numarul de variabile de intrare si de iesire :
sisteme monovariabile; sisteme multivariabile
510) Clasificarea sistemelor automate dupa natura semnalelor prelucrate de sistemul automat :
sisteme automate continue; sisteme numerice;
511) Teoria sistemelor automate se ocupa cu :
a,b si c
512) Functia de transfer pentru un element proportional
513) Functia de transfer pentru un element de ordinul I
514) Functia de transfer pentru un element de ordinul II
515) Functia de transfer pentru un element de ordinul III
nici-o variant
516) Timpul de raspuns al unui sistem est
timpul dupa care valoarea absoluta a diferentei dintre marimea de iesire si valoarea ei de regim stationar devine mai mica si se mentine sub o anumita limita
517) Circuitul din figura58 realizeaza functia
518) Figura52 prezinta simbolul unui
AND (SI)
519) Figura53 prezinta simbolul unui
NAND (SI negat)
520) Figura54 prezinta simbolul unui
ENOR (SAU exclusiv negat)
521) Figura55 prezinta simbolul unui
EOR (SAU exclusiv)
522) Figura56 prezinta simbolul unui
OR (SAU)
523) Figura57 prezinta simbolul unui
NOR (SAU negat)
524) O memorie RAM este o memorie cu access de _________:
citire si scriere
525) O memorie ROM este o memorie _________
Nevolativa
526) Procesoarele sunt automate de ordinul ____
III sau mai mare
527) Arhitectura minimala a unui calculator este formata din :
procesor, memorie (RAM, ROM), bus de semnale, porturi de I/O
528) Porturile de I/O sunt cuplate la procesor prin intermediul _______
bus-ului procesor de date, adrese si semnale de comanda si contro
529) Procesorul este format din :
a si b
530) Microprocesorul Intel PIV este realizat in tehnologie
VLSI
531) Indicatorul Z (zero -Flag) al RALU indica
In urma unei operatii aritmetica sau logice rezultatul a fost nul
532) Indicatorul CY (Carry -Flag) al RALU indica
A aparut un transport de iesire din cel mai semnificativ bit al rezultatului in urma unei operatii aritmetice(logice
533) Indicatorul S (S - Sign) al RALU
In urma unei operatii aritmetice intre numere cu semn, rezultatul este negative
534) Indicatorul H (H- Half carry) al RALU
S-a realizat un transfer de la bitul 4 la bitul 5 in urma operatiei de scadere
535) Dimensiunea acumulatorului dintr-un microprocesor de 8 biti
1 Byte
536) Cati biti are un Byte
8 biti
537) Cea mai mica unitatea informationala de transport
Bit
538) Unitatea de decodofocare a instructiunilor este ______ .
un circuit logic combinational (CLC)
539) Contorul de adrese de program este numit ____ :
PC ( program counter) register
540) Procesorul acceseza programul executat curent din _______
segmentul de memorie alocat programului ce se afla in executie
541) Tastatura este ________
un periferic de interfata a calculatorului cu operatorul uman
542) Denumirea primului ciclu masina:
FETCH
543) Se aplica un semnal sinusoidal la intrarea unui amplificator functionand in clasa A. Unghiul de conductie al elementului amplificator este:
360grd;
544) Se aplica un semnal sinusoidal la intrarea unui amplificator functionand in clasa AB. Unghiul de conductie al elementului amplificator este:
cuprins intre 180 grd si 360grd;
545) Se aplica un semnal sinusoidal la intrarea unui amplificator functionand in clasa B. Unghiul de conductie al elementului amplificator este:
180grd
546) Se aplica un semnal sinusoidal la intrarea unui amplificator functionand in clasa C. Unghiul de conductie al elementului amplificator este:
mai mic de 180grd;
547) Figura27 prezinta:
schema bloc a unui amplificator cu reactie serie parallel
548) Figura28 prezinta:
schema bloc a unui amplificator cu reactie paralel parallel
549) Figura29 prezinta:
schema bloc a unui amplificator cu reactie paralel serie
550) Figura30 prezinta:
schema bloc a unui amplificator cu reactie serie serie
551) In mod uzual amplificatorul electronic este definit cu ajutorul schemei bloc din figura 40. Marimea ?xi? reprezinta
valoarea instantanee a semnalului de intrare sau excitatie
552) Marimea ?xo? din figura 40 reprezinta
valoarea instantanee a semnalului de iesire sau raspuns
553) Marimea ?a? din figura 40 reprezinta
amplificarea amplificatorului
554) in practica, sunt tranzistoarele din amplificatoarele in contratimp clasa B au jonctiunea baza - emitor prepolarizata direct astfel ca prin fiecare tranzistor sa circule un mic curent de repaus. Despre aceste amplificatoare se spune ca lucreaza in clasa AB. Prin aceasta se urmareste:
reducerea distorsiunii de trecere
555) Variatoarele de tensiune continue sunt de obicei utilizate pentru:
reglarea turatiilor masinilor electrice de curent continuu
556) Ce particularitate au invertoarele de comutatie fortata fara de cele cu comutatie naturala?
au circuite auxiliare pentru blocarea dispozitivelor semi-conductoare
557) Ce rol are condensatorul din schema invertorului Wagner?
de a furniza energia reactiva necesara comutatiei
558) Ce caracteristica principala au invertoarele autonome de tensiune trifazate?
blocarea tiristorului principal se realizeaza prin amorsarea unui alt tiristor principal
559) Variatorul de tensiune continua pentru patru cadrane, permite functionarea motorului de curent continuu astfel
in regim de motor, generator, in ambele sensuri de rotatie
560) Un amplificator operational lucrand in bucla inchisa (cu reactie negativa) are amplificarea in tensiune intotdeauna:
determinata de reteaua de reactive
561) Figura22 prezinta configuratia standard de stabilizator serie cu reactie. Blocul notat AE – amplificatorul de eroare - are rolul:
de a compara compara nivelul de tensiune cules de reteaua de reactie cu nivelul de tensiune al sursei de referinta si a genera un semnal proportional cu diferenta dintre ele (amplifica semnalul de eroare).
562) Figura22 prezinta configuratia standard de stabilizator serie cu reactie. Blocul notat UREF – tensiunea de referinta- are rolul
de a asigura un nivel constant al tensiunii pe care o genereaza
563) Figura22 prezinta configuratia standard de stabilizator serie cu reactie. Rezistorii R1 si R2 au rolul
de a asigura reactia negative
564) Figura22 prezinta configuratia standard de stabilizator serie cu reactie. TR – tranzistorul regulator - are rolulunei rezistente variabile, astfel incat tensiunea pe sarcina sa fie mentinuta constanta
565) Figura23 prezinta exemplul tipic de stabilizator serie cu reactie. Grupul R3, Dz are rolul
de sursa de referinta
566) Figura23 prezinta exemplul tipic de stabilizator serie cu reactie. Grupul R4, T1 are rolul
de amplificator de eroare
567) Figura23 prezinta exemplul tipic de stabilizator serie cu reactie. Tranzistorul T2 are rolul
de element regulator
568) Figura23 prezinta exemplul tipic de stabilizator serie cu reactie. Grupul R1, R2 are rolul
de retea de reactive
569) Figura25 prezinta un stabilizator cu dioda Zener imbunatatit. Cea de a doua celula de stabilizare are rolul de
mari factorul de stabilizare
570) Figura26 prezinta un stabilizator cu dioda Zener imbunatatit. Tranzistorul T are rolul de a
mari curentul de iesire
571) Pentru amplificatorul de tensiune
atat semnalul de excitatie cat si semnalului de raspuns reprezinta tensiuni
572) Pentru amplificatorul de curent
atat semnalul de excitatie cat si semnalului de raspuns reprezinta curenti
573) Pentru amplificatorul transrezistenta (tranzimpedanta)
semnalul de excitatie este curent iar cel de raspuns tensiune
574) Pentru amplificatorul transconductanta (transadmitanta)
semnalul de excitatie este tensiune iar cel de raspuns current
575) Figura31 prezinta un amplificator cu reactie. in acest caz reactia este de tipul:
paralel parallel
576) Figura32 prezinta un amplificator cu reactie. in acest caz reactia este de tipul:
serie serie
577) Figura33 prezinta un amplificator cu reactie. in acest caz reactia este de tipul:
serie parallel
578) Figura34 prezinta un amplificator cu reactie. in acest caz reactia este de tipul:
paralel serie
579) Figura41 prezinta schema echivalenta ideala pentru
amplificatorul de tensiune
580) Figura42 prezinta schema echivalenta ideala pentru
amplificatorul de current
581) Figura43 prezinta schema echivalenta ideala pentru
amplificatorul transrezistenta
582) Figura44 prezinta schema echivalenta ideala pentru
amplificatorul transconductanta
583) Figura45 prezinta schema echivalenta uzuala pentru amplificatorul de tensiune. Despre rI si ro se poate spune:
rI are valori foarte mari in timp ce r0 este foarte mic
584) Figura46 prezinta schema echivalenta uzuala pentru amplificatorul de tensiune. Despre rI si ro se poate spune:
585)
rI are valori foarte mici in timp ce r0 este foarte mare
586) Figura47 prezinta schema echivalenta uzuala pentru amplificatorul de tensiune. Despre rI si ro se poate spune:
atat rI cat si ro sunt foarte mici
587) Figura48 prezinta schema echivalenta uzuala pentru amplificatorul de tensiune. Despre rI si ro se poate spune:
atat rI cat si ro sunt foarte mari
588) Castigul in tensiune al unui amplificator de tensiune se masoara in
dB
589) Castigul in curent al unui amplificator de curent se masoara in
dB
590) Amplificarea transimpedanta a unui amplificator transimpedanta se masoara in
Ohm
591) Amplificarea transadmitanta a unui amplificator transadmitanta se masoara in
S
592) Considerand RB>>rz rezistenta de iesire a circuitului de stabilizare din figura 14, este aproximativ
Rz
593) Pentru etajul emitor comun prezentat in figura 15, considerand RC<
594) in prezenta unei reactii negative globale aplicata unui amplificator construit din mai multe etaje, valoarea raportului S/N (semnal/zgomot) masurata la iesire este:
mai mare;
595) Reactia negativa aplicata unui etaj de amplificare face ca valoarea raportului S/N (semnal/zgomot) masurata la iesire sa fie:
Neschimbata
596) Randamentul unui amplificator ideal in clasa A (figura 16), avand sarcina cuplata prin transformator este:
50%;
597) in figura 17 este reprezentata schema de principiu a unui un amplificator in contratimp cu tranzistoare identice functionand in clasa B. Excursia maxima de tensiune este:
2EC;
598) in figura 17 este reprezentat un amplificator in contratimp cu tranzistoare identice functionand in clasa B. Randamentul amplificatorului este aproximativ
78 %;
599) Pentru etajul emitor comun prezentat in figura 15 rezistenta de intrare, in regim cvasistatic de semnal mic, este
Rin@ rp
600) Pentru etajul emitor comun prezentat in figura 15 rezistenta de iesire, in regim cvasistatic de semnal mic, este:
Ro@Rc
601) Pentru etajul emitor comun prezentat in figura 15 frecventa superioara de lucru este:
ωH≤ωβ
602) Pentru etajul colector comun prezentat in figura 18 amplificarea in tensiune U0/Ein, in regim cvasistatic de semnal mic, este:
Au~1
603) Pentru etajul colector comun prezentat in figura 18 rezistenta de intrare, in regim cvasistatic de semnal mic, este:
604) Pentru etajul colector comun prezentat in figura 18 rezistenta de iesire (cu intrare in scurtcircuit), in regim cvasistatic de semnal mic, este
605) Pentru etajul baza comuna prezentat in figura19 amplificarea in tensiune U0/Uin, in regim cvasistatic de semnal mic (considerand RC<
606) Pentru etajul baza comuna prezentat in figura 19 rezistenta de intrare, in regim cvasistatic de semnal mic, este:
607) Pentru etajul baza comuna prezentat in figura 19 rezistenta de iesire (cu intrare in scurtcircuit), in regim cvasistatic de semnal mic, este:
Ro~Rc
608) Pentru etajul baza comuna prezentat in figura 19 frecventa superioara de lucru este:
ωH≤ωT
609) Schema din figura 20 prezinta un amplificator inversor construit cu ajutorul unui amplificator operational. Amplificarea in tensiune este:
610) Schema din figura 21 prezinta un amplificator neinversor construit cu ajutorul unui amplificator operational. Amplificarea in tensiune este
611) Figura24 prezinta un stabilizator cu dioda Zener. in functionare normala iZ indeplineste conditia
612) Coeficientul de stabilizare al stabilizatorului din figura 24 este aproximativ
613) Rezistenta de iesire a stabilizatorului din figura 24 este aproximativ
614) Figura35 prezinta schema unui amplificator sumator. Tensiunea de iesire are expresia
615) Figura36 prezinta schema unui circuit de integrare. Tensiunea de iesire are expresia
616) Figura37 prezinta schema unui circuit de derivare. Tensiunea de iesire are expresia
617) Figura38 prezinta schema unui circuit de logaritmare. Tensiunea de iesire are expresia
618) Figura39 prezinta schema unui circuit de antilogaritmare. Tensiunea de iesire are expresia
619) Impedanta de intrare in regim cvasistatic de semnal mic a unui amplificator de tensiune se determina
introducand o sursa de test la intrare, iesirea fiind lasata in gol
620) Impedanta de intrare in regim cvasistatic de semnal mic a unui amplificator de curent se determina
introducand o sursa de test la intrare, iesirea fiind scurtcircuitata
621) Impedanta de intrare in regim cvasistatic de semnal mic a unui amplificator transimpedanta se determina
introducand o sursa de test la intrare, iesirea fiind lasata in gol
622) Impedanta de intrare in regim cvasistatic de semnal mic a unui amplificator transadmitanta se determina
introducand o sursa de test la intrare, iesirea fiind scurtcircuitata
623) Impedanta de iesire in regim cvasistatic de semnal mic a unui amplificator de tensiune se determina
introducand o sursa de test la intrare, iesirea fiind scurtcircuitata
624) Impedanta de iesire in regim cvasistatic de semnal mic a unui amplificator de curent se determina
introducand o sursa de test la intrare, iesirea fiind lasata in gol
625) Impedanta de iesire in regim cvasistatic de semnal mic a unui amplificator transimpedanta se determina
introducand o sursa de test la intrare, iesirea fiind lasata in gol
626) Impedanta de iesire in regim cvasistatic de semnal mic a unui amplificator transadmitanta se determina
introducand o sursa de test la intrare, iesirea fiind scurtcircuitata
627) Pentru un tranzistor bipolar in regim de blocare
ambele jonctiuni sunt polarizate invers
628) Pentru un tranzistor bipolar in regim saturat
ambele jonctiuni sunt polarizate direct
629) Pentru un tranzistor bipolar in regim activ normal inversat
jonctiunea colectorului este polarizata direct, iar jonctiunea emitorului este polarizata invers
630) In regim de blocare
tranzistorul bipolar se comporta ca un circuit interrupt
631) In regim saturat
tranzistorul bipolar se comporta ca un scurt circuit
632) In regim activ normal
apare efectul de transistor
633) In regim activ normal inversat
tranzistorul nu se foloseste
634) In conditii normale, o dioda stabilizatoare functioneaza
in regim de polarizare inversa la tensiunea de strapungere V(BR)
635) Tranzitia din starea de blocare in starea de conductie (amorsarea sau aprinderea) unui tiristor se face prin
comanda de pe poarta si polarizarea directa a structurii (plus pe anod minus pe catod).
636) Blocarea tiristorului se face
actionand in circuitul de forta prin reducerea curentului principal
637) Figura6 prezinta simbolul unui
TECMOS cu canal indus n
638) Figura7 prezinta simbolul unui:
TECMOS cu canal indus p
639) Figura8 prezinta simbolul unui:
TECMOS cu canal initial n
640) Figura9 prezinta simbolul unui
TECMOS cu canal initial p
641) Mecanismul strapungerii intr-o dioda de referinta (stabilizatoare) este:
uneori strapungere Zener, alteori strapungere prin avalansa si cateodata o combinatie a ambelor